Why does my cat need vaccines if they're only going to stay indoors? - The Waggin' Train Veterinary Clinic

Some are public health concerns. Rabies. I know that your cat is only going to get rabies by being exposed to a rabid animal. It's probably not going to happen indoors, but what happens if your window pops open, or your window is open and the screen pops out and your cat wants to take off? You can't afford to risk those types of things. A disease like rabies, for example, is a human threat. If, by some chance, your cat gets out, gets bitten by a rabid animal, and comes back home, they will likely act fine for quite a while. But then on about day 9 or 10, your cat is not acting quite so fine. You see where I'm going with that? There's no point in allowing that to even be a possibility.

So for certain public health concerns, there's that. And again, even other viruses that I didn't mention in that scenario could involve the same exact thing happening. Say your cat's indoors and you think to yourself, "Oh, I don't want to do feline leukemia." What happens if he gets out? What happens if it's a pretty fall day and there's another cat that comes nose to nose with him at the screen. They didn't even come into direct contact, but can it be transmitted that way? You bet it can. So that's the reason why it's still important.